Temozolomide, 3-methyl-8-aminocarbonyl-imidazo[5,1-d]-1,2,3,5-tetrazin-4(3H)-one, is a known antitumor drug; see for example Stevens et al., J. Med. Chem. 1984, 27, 196-201, and Wang et al., J. Chem. Soc., Chem. Commun., 1994,1687-1688. Temozolomide, the compound of formula 1: is described in U.S. Pat. No. 5,260,291 (Lunt et al.).
The synthesis of 1 by the process described in J. Med. Chem. 1984, 27, 196-201 is depicted in the scheme I below. 
In this process, 5-amino-1H-imidazole-4-carboxamide (A) is converted into 5-diazo-1H-imidazole-4-carboxamide (B), which is then cyclized with methylisocyanate in dichloromethane to provide a high yield of temozolomide. However, this process requires isolation of the unstable and potentially dangerous 5-diazo-1H-imidazole-4-carboxamide (B). Moreover, methylisocyanate is a difficult reagent to handle and ship, especially on the industrial scale, and indeed is better avoided in industrial manufacture. Furthermore, the cycloaddition of methylisocyanate requires a very long reaction time: Table I in J. Med Chem. 1984, 27,196-201, suggests 20 days. Additionally, Stevens et al mention that the cycloaddition of the methylisocyanate to the compound of the formula (B) can proceed through two different intermediates:
The production of I by the two processes described in J. Chem. Soc., Chem. Commun., 1994, 1687-1688 provides a low overall yield from 5-amino-1H-imidazole-4-carboxamide (A): less than 20% (unoptimized—about 17% through 5-diazo-1H-imidazole-4-carboxamide (B) and about 15% through 5-amino-N1-(ethoxycarbonylmethyl)-1H-imidazole-1,4-dicarboxamide (C)); Scheme II below: 
Moreover, the unstable 5-diazo-1H-imidazole-4-carboxamide (B) still has to be isolated in the branch of this process that uses it as an intermediate.
Clearly, therefore, there is a need for synthetic methods that:                a) are more convenient and higher yielding, especially on commercial scale;        b) approach the synthesis of the temozolomide nucleus in novel ways; or        c) improve the preparation or use of intermediates for the processes.        